In some medical procedures, surgical instruments may be tracked by imaging the position of the instrument in real-time with respect to the surrounding anatomy. For example, in one conventional method, a position of a catheter is continuously monitored by two-dimensional (2D) x-ray fluoroscopy, and the surrounding tissue (e.g., vasculature) is visualized with contrast agent injections. Because of the continuous x-ray imaging, however, the total dose of ionizing radiation received by the patient during this procedure can be a concern. In addition, nearby personnel are required to wear lead aprons to limit exposure to the ionizing radiation.
Other imaging modalities have been proposed for tracking surgical instruments, but these imaging modalities have certain problems or drawbacks such as high cost of equipment and/or operation, long acquisition times, substantial hardware or equipment modifications, or poor quality of images. For example, magnetic resonance imaging (MRI) has been used to track surgical instruments. Generally, MRI can provide high resolution 3D images with excellent contrast of the surrounding anatomy. However, surgical tracking using MRI can be expensive, may have a low acquisition rate, and may provide limited access to the patient compared to X-ray fluoroscopy. Moreover, any surgical instrument used in the procedure must be non-ferrous, potentially limiting the instruments available to the surgeon.
Ultrasound is another non-invasive imaging technology that has been applied to catheter tracking. One challenge with ultrasound tracking is that the catheter operates as a specular reflector. Therefore, it is often necessary to modify the catheter in some way, such as placing a transducer on the tip, in order to visualize the catheter position in ultrasound. This can add to the bulk and cost of the instrument.
Accordingly, systems and methods for tracking surgical instruments without using imaging modalities that can be harmful to the patient or require costly equipment are generally desired. Magnetic particle imaging (MPI) is a recently developed imaging modality in which a spatial distribution of magnetic particles can be determined. For example, MPI is capable of imaging a distribution of superparamagnetic iron oxide particles (SPIOs) with a relatively high sensitivity, high spatial resolution, and high imaging speed. In particular, MPI detects the magnetization change caused when a sensitive region passes through the sample (e.g., a region in which there is little or no magnetic field surrounded by a larger saturating field). Unlike other imaging modalities, MPI is free of ionizing radiation. However, the known MPI systems are directed to imaging a single point and moving that point relative to the object-of-interest. With a sensitive point configuration, image acquisition is inherently three dimensional which can therefore result in significantly long acquisition times. Accordingly, a system for acquiring three dimensional images of magnetic material in less time than conventional MPI systems is desired.